Environmental Engineering Reference
In-Depth Information
(c)
Electricity
Low-pressure steam
Air cooled
condenser
Generator
Turbine
High-pressure steam
Air out
Air out
Fan
Air in
Air in
Boiler
Boiler water
Heat source
(d)
Electricity
Generator
Low-pressure steam
Fan
Evaporation
High-
pressure
steam
Low-
pressure
steam
Cooling
tower
Cool
cooling
water
Turbine
Small
amount
of makeup
water
Air out
Air out
Fan
Steam
valve
Boiler
Air in
Air in
Ambient
air
Ambient
air
Warm
cooling water
Condenser
Boiler water
Lake
Boiler water
Heat source
FIGURE 28.7 (Continued)
Cooling schemes for thermoelectric power plants. (c) Air cooling uses fans to blow air past heat exchanger to
cool steam. (d) Hybrid cooling uses dry cooling when conditions allow eficiency to remain high, or employs
water spray over the condensing tubes when conditions lead to increase in required cooling capacity. Some
hybrid cooling schemes use water spray at all times. (From USGAO,
Energy-Water Nexus: Improvements to Federal
Water Use Data Would Increase Understanding of Trends in Power Plant Water Use
. US Government Accountability
Ofice, 2009.)
use of microchannel heat exchangers. In their work, distinct low regimes within micro-
tubes (dimensions in the submillimeter range) were identiied as opposed to conventional
heat exchangers. In a test system, with 200 MW of waste heat input, 140 MW of cooling
load was obtained with nearly 90 MW cooling at 5°C with an electrical input of 23 MW [19].
Wet recirculating systems reuse cooling water and use either cooling towers or cool-
ing ponds to allow the water temperature to decrease. These systems require <5% of the
withdrawal of a once-through system, yet consume almost all of the water withdrawn [15].
The last two types of cooling schemes, dry and hybrid cooling, are considered advanced
cooling methods in contrast to the widely implemented wet methods as discussed above.
Dry cooling uses fans and/or blowers to create air low past steam condenser tubes; hence,
